*{
    margin: 0;
    padding: 0;
}
a{
   text-decoration: none;
    color: #000;
}
.button1{
    display: inline-block;
    height: 50px;
    line-height: 50px;
    width: 100px;
    border: 1px solid #ccc;
    margin: 20px;
    text-align: center;
    border-radius: 20px;
}
.button1:hover{
    background: skyblue;
}
.button2{
    display: inline-block;
    height: 50px;
    line-height: 50px;
    width: 100px;
    border: 1px solid #ccc;
    margin: 20px;
    text-align: center;
    border-radius: 20px;
}
.button2:hover{
    background: skyblue;
}
.button3{
    display: inline-block;
    height: 50px;
    line-height: 50px;
    width: 100px;
    border: 1px solid #ccc;
    margin: 20px;
    text-align: center;
    border-radius: 20px;
}
.button3:hover{
    background: skyblue;
}
.box{
    height: 650px;
    border: 1px solid #ccc;
    margin-left: 20px;
}
.content1{
    height: 200px;
    border: 1px solid red;
    margin: 10px;
}
.content2{
    display: none;
    height: 200px;
    border: 1px solid red;
    margin: 10px;
}
.content3{
    display: none;
    height: 200px;
    border: 1px solid red;
    margin: 10px;
}